1. Field of the Invention
The present invention relates to an on-vehicle electronic control device such as an on-vehicle engine control device and an on-vehicle transmission control device, and more particularly, to an improved on-vehicle electronic control device capable of preventing an abnormal operation from occurring through improper connection of an on-vehicle battery in a reverse polarity and through abnormal contact of part of load wiring to a power supply line, which causes a short-to-power current to flow through a sneak path.
2. Description of the Related Art
In general, at least two systems of power feeding circuits are used as power feeding circuits for an on-vehicle electronic control device. One system is a power feeding circuit for a constant voltage power supply that is fed power from an on-vehicle battery so as to supply a predetermined stable control voltage to a microprocessor that controls drive of a plurality of on-vehicle electrical loads via a plurality of load switching elements in response to an operation state of an input sensor group and the content of a cooperating program memory.
The other system is a power feeding circuit for the plurality of load switching elements that are controlled to be switched by the microprocessor. The load switching elements are connected to the plurality of on-vehicle electrical loads, which are connected to an external part of the on-vehicle electronic control device, to thereby control the drive of the plurality of on-vehicle electrical loads.
For example, referring to FIG. 3 of “ON-VEHICLE POWER SUPPLY CONTROL DEVICE” in Japanese Patent Application Laid-open No. 2011-020522 illustrated in FIG. 13, in an on-vehicle power supply control device 10, an IG relay 23 and an ACC relay 24 are provided between an input terminal 11 connected to a battery and output terminals 14 and 15 connected to ECUs 50a to 50c corresponding to the on-vehicle electronic control devices, and a control circuit 27 controls on/off of the IG relay 23 and the ACC relay 24 based on information relating to a connection state of an ignition switch and an accessory switch of a vehicle, which is received by a communication circuit 28.
Further, only fuses 26 are connected between the input terminal 11 connected to the battery and output terminals 13 connected to the ECUs 50a to 50c corresponding to the on-vehicle electronic control devices (detailed connection is omitted in FIG. 13), and a step-down circuit 22 and current limiting circuits 25 are provided between the input terminal 11 and output terminals 12 to supply a constant DC voltage of 5 V.
Therefore, in a case of an on-vehicle electronic control device without an accessory-related electrical load, the on-vehicle electronic control device includes two systems of power feeding circuits, specifically, a power feeding circuit for driving an ignition-switch-related electrical load and a power feeding circuit for feeding power to the microprocessor in the on-vehicle electronic control device.
Note that, in the on-vehicle electronic control device that requires not only DC 5 V but also various constant voltages, it is necessary to use any one of the output terminals 13 to 15 instead of the output terminal 12 so that power is fed to various constant voltage power supplies in the on-vehicle electronic control device.
Note that, when an electromagnetic relay in which a diode is connected in series to an exciting coil is used as the IG relay 23 and the ACC relay 24, the electromagnetic relay is not energized in a case where the connection polarity of the on-vehicle battery is improper, and hence the output contact thereof is not closed. Therefore, the electromagnetic relay has both the reverse connection preventing function for an abnormal state and the energization switching function for a normal state.
On the other hand, regarding the load switching element, a field effect transistor has a low internal resistance and small temperature rise even when a large current flows, and hence the field effect transistor is often used as a switching element for a power circuit.
Further, it is well known to use a non-contact switching element in which a pair of field effect transistors is connected in series so that energization directions of the internal parasitic diodes thereof are opposite to each other, to thereby have a reverse connection protecting function and a switching element function.
However, the field effect transistor has a parasitic diode that is connected in parallel in an opposite direction to the energization direction. Therefore, there occurs a short-to-power abnormality in which the output side of the transistor is abnormally brought into contact with a positive power supply line. When the power supply on the input side of the transistor is interrupted, there is a problem in that power is fed through a sneak path from a short-to-power power supply to the input of the transistor.
For example, referring to FIG. 4 of “POWER SUPPLY REVERSE CONNECTION PROTECTING CIRCUIT” in Japanese Patent Application Laid-open No. 2007-082374 illustrated in FIG. 14, in an ECU 45 corresponding to the on-vehicle electronic control device that operates based on the power of a battery 3, an N-channel FET 21 is provided on power supply wiring 15 that connects a power supply terminal 5 connected to a positive terminal of the battery 3 to a control circuit 13 to be supplied with power so that an anode of a parasitic diode D1 thereof is provided on the power supply terminal 5 side. Further, on the downstream side of the FET 21, an N-channel FET 22 is provided so that a cathode of a parasitic diode D2 thereof is provided on the FET 21 side.
Then, in a case where an ignition key switch 9 is turned on when the battery 3 is connected normally, the FETs 21 and 22 are turned on by charge pump circuits 43 and 47 supplied with operation power from the drain side of the FET 21. Thus, power of the battery 3 is supplied to the control circuit 13.
Further, when the battery 3 is connected reversely, the FETs 21 and 22 are turned off to block a reverse current by the parasitic diode D1.
Note that, the control circuit 13 carries out processing for controlling a control target (on-vehicle device such as an engine and a transmission) and driving of an actuator. The control circuit 13 includes a power supply circuit (not shown) for generating a constant power supply voltage (for example, 5 V) from a battery voltage VB input through the power supply wiring 15, various ICs 19 such as a microcomputer that operates by receiving the power supply voltage generated by the power supply circuit, and an output circuit (not shown) for driving the actuator based on a signal from the IC 19 (based on paragraph 0042).
Further, the control circuit 13 starts its operation when the FET 22 turns on so that the control circuit 13 receives power from the battery 3. When the control circuit 13 starts its operation, a drive signal Sd is output so that the FETs 21 and 22 are maintained in the on state even if the ignition key switch 9 is turned off (based on paragraph 0056).
Further, although not shown, the control circuit 13 monitors the voltage of a signal input terminal 11 in order to detect the on/off state of the ignition key switch 9.
Then, the control circuit 13 detects that the ignition key switch 9 has been turned off based on the voltage of the signal input terminal 11. After that, when the operation stop preprocessing such as data saving is ended and a condition that allows operation stop is satisfied, the output of the drive signal Sd is stopped (based on paragraph 0057).
In Japanese Patent Application Laid-open No. 2011-020522 described above, when there occurs such a short-to-power abnormality that load wiring from the ECUs 50a to 50c corresponding to the on-vehicle electronic control devices to the on-vehicle electrical loads is abnormally brought into contact with the power supply wiring connected to the output terminal 14, even if the IG relay 23 is closed, the short-to-power power is fed through a sneak path into the output wiring of the IG relay 23 to cause the following problems.
The first problem is a power wasting and malfunction problem. Even when the IG relay 23 is interrupted, power is erroneously fed to each of the combined on-vehicle electronic control devices (ECU 50a to ECU 50c). Thus, power is wasted and the on-vehicle electronic control device malfunctions.
The second problem is a component damage problem. An excess current flows through the parasitic diode inside the load switching element at a position in the sneak path of the short-to-power power to burn out the load switching element.
The third problem is as follows. When the drive circuit of the IG relay 23 has an abnormality determination function, the output voltage is generated even if the exciting coil of the IG relay 23 is not energized, and hence occurrence of a welding abnormality of the output contact may be erroneously determined.
The fourth problem is another power wasting and malfunction problem. When the constant voltage power supply is connected in a branched manner from the output terminal 14 of the IG relay 23, the short-to-power power is fed through a sneak path as the input voltage of the constant voltage power supply.
In Japanese Patent Application Laid-open No. 2007-082374 described above, the twin switching elements 21 and 22 are provided in a non-contact form in which the N-channel or P-channel field effect transistors are connected in series and the energization directions of the parasitic diodes thereof are set to be opposite to each other, to thereby provide the reverse connection protecting function corresponding to the electromagnetic relay and the switching element function. The twin switching elements 21 and 22 are incorporated in the ECU 45 corresponding to the on-vehicle electronic control device so as to feed power to the constant voltage power supply for driving the microprocessor and also feed power in a branched manner to the output circuit for driving the actuator.
Therefore, when a short-to-power abnormality occurs on the load wiring for the on-vehicle electrical load, even if the ignition key switch 9 that is a power supply switch is opened, the short-to-power power is fed through a sneak path as power for the constant voltage power supply or other load circuits whose power is fed from the same twin switching elements 21 and 22, with the result that the above-mentioned first to fourth problems occur.